1. Field of the Invention
The present invention relates to a honeycomb structure, an exhaust gas cleaning unit, and a manufacturing method of the honeycomb structure.
2. Description of the Related Art
Conventionally, various techniques have been developed to clean vehicle exhaust gas, however, sufficient countermeasures have not been taken for the increasing traffic. Emission restrictions will become tighter not only in Japan but all over the world. In particular, a restriction of NOx in diesel exhaust gas is becoming very strict. A conventional method to reduce NOx by controlling an engine combustion system is not sufficient anymore. As a diesel NOx cleaning system for such problems, there is a NOx reduction system (called an SCR system) using ammonia as a reducing agent. Moreover, zeolite is known as a material to adsorb the ammonia used in the SCR system.
International Publication No. 06/137160 discloses a honeycomb structure having a honeycomb unit including a ceramic particle, and an inorganic fiber and/or a whisker, with a cross-sectional area of 5 to 50 cm2 vertical to a longitudinal direction of the honeycomb unit and circularity of 1.0 to 2.5 mm of the cross-section vertical to the longitudinal direction of the honeycomb unit. In this case, one or more ceramic selected from alumina, silica, zirconia, titania, ceria, mullite, and zeolite is employed as an example.
Note that a honeycomb structure which has a retention seal over an outer surface and is housed in a metal container formed of stainless steel or the like is used as an exhaust gas cleaning unit in general.
The entire contents of International Publication No. 06/137160 are incorporated herein by reference.